Phytotoxicity of a Chemical Weapon Simulant, Triethyl Phosphate

Triethyl phosphate (TEP) is proposed to be used as a chemical weapon simulant in missile testing at White Sands Missile Range in New Mexico. Studies were conducted to determine the phytotoxicity of TEP using sorghum-sudangrass [Sorghum bicolor (L.) Moench], tomato (Lycopersicon lycopersicum Mill.), and glossy privet (Ligustrum lucidum Ait.) as test plants grown on Mimbres-Glendale (MG) and Nickel-Tencee (NT) soil associations obtained from White Sands Missile Range. Triethyl phosphate was applied to soil and foliar tissue at rates of 0, 4, 400, and 40 000 mg m⁻² soil surface. Triethyl phosphate also was applied in a thickened formulation, as used in missile testing, at an application rate of 40 000 mg m⁻² on both soil and foliar tissue. Toxicity was only observed at the highest application rate with pure and thickened TEP. The method of TEP application to soil or foliar tissue did not affect the dry matter weight of tomato or glossy privet growth. There were inconsistent effects of TEP application method on sorghum-sudangrass dry matter weight, depending on soil type. Triethyl phosphate affected the test plants differently with resistance to TEP toxicity increasing in the order: tomato ≃ sorghum-sudangrass on NT soil < sorghum-sudangrass on MG soil < glossy privet. A seedling emergence study using sorghum-sudangrass, tomato, and cucumber (Cucumis sativus L.) resulted in similar conclusions from the whole plant studies showing TEP toxicity only at the highest application rate of 40 000 mg m⁻². There were indications from sorghum-sudangrass growth and cucumber seedling emergence that TEP toxicity may be less on soil having a higher clay and organic matter content, which may have been due to TEP sorption in soil and decreased TEP bioavailability to plant roots. The absence of phytotoxicity symptoms indicated plants would not be harmed if application rates were at or below 400 mg TEP m⁻².